Well, as it turns out, I'm living proof that PM use can result in speedy and dramatic changes. Although the changes are "subtle", if I showed by girlfriend and asked her to compare my chest to her last detailed memory of it, I'm sure she'd realize things have changed. If I asked her to grab them and feel the (now large) lumps behind my (now larger) nipples, she'd be really surprised.
And I'm surprised because all of this happened very quickly. 5 or 6 days off of PM and I think I'm still growing. And here's the thing: I'm much more interested in my boobs without PM in my system. More male hormones makes me more horny. And more horny means I want boobs to play with.
I think that's the cycle you have to watch out for. That's the trap. That's what's ahead.